Context: The clinical relevance of medullary thyroid microcarcinoma, a calcitonin-secreting malignancy, as a valid target for biochemical screening programs has been called into doubt.
Objective: This investigation aimed at clarifying the intensity of lymphatic spread and exploring the potential for biochemical cure in medullary thyroid microcarcinoma.
Design: This was a retrospective analysis.
Setting: The setting was a tertiary referral center.
Patients: Included were 233 patients with hereditary (126 patients) or sporadic (107 patients) medullary thyroid microcarcinoma.
Interventions: The intervention was compartment-oriented surgery.
Main outcome measure: Clinical-histopathological variables were stratified by primary tumor diameter (2-mm increments) and biochemical cure.
Results: With incremental tumor diameter, increasingly more patients with medullary thyroid microcarcinoma harbored lymph node metastases: from 6 to 62% of patients (P < 0.001) for hereditary and from 13 to 43% of patients (P = 0.01) for sporadic disease. The corresponding biochemical cure rates declined from 96 to 71% (P = 0.001) and from 85 to 77% (P = 0.01). Distant disease (two instances of lung metastasis and one instance of bone and liver metastasis) was exceptional, affecting 1.3% of patients with medullary thyroid microcarcinoma. Strongest predictors of a patient's failure to achieve normal calcitonin serum levels were positive nodal status (79 vs. 11% in hereditary and 79 vs. 12% in sporadic disease; both P < 0.001) and the number of involved nodes (means of 6.6 vs. 0.3 nodes in hereditary and 8.8 vs. 0.4 nodes in sporadic disease; both P < 0.001).
Conclusions: Sporadic and hereditary medullary thyroid microcarcinoma carry a significant risk of lymph node metastasis and postoperative calcitonin elevation.